Gate structures in semiconductor devices

ABSTRACT

A semiconductor device with different configurations of gate structures and a method of fabricating the same are disclosed. The method includes forming a fin structure on a substrate, forming a gate opening on the fin structure, forming a metallic oxide layer within the gate opening, forming a first dielectric layer on the metallic oxide layer, forming a second dielectric layer on the first dielectric layer, forming a work function metal (WFM) layer on the second dielectric layer, and forming a gate metal fill layer on the WFM layer. The forming the first dielectric layer includes depositing an oxide material with an oxygen areal density less than an oxygen areal density of the metallic oxide layer.

BACKGROUND

With advances in semiconductor technology, there has been increasing demand for higher storage capacity, faster processing systems, higher performance, and lower costs. To meet these demands, the semiconductor industry continues to scale down the dimensions of semiconductor devices, such as metal oxide semiconductor field effect transistors (MOSFETs), including planar MOSFETs, fin field effect transistors (finFETs), and gate-all-around (GAA) FETs. Such scaling down has increased the complexity of semiconductor manufacturing processes.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of this disclosure are best understood from the following detailed description when read with the accompanying figures.

FIG. 1A illustrates an isometric view of a semiconductor device, in accordance with some embodiments.

FIGS. 1B-1E illustrate cross-sectional views of a semiconductor device with different gate structures, in accordance with some embodiments.

FIG. 1F illustrates device characteristics of a semiconductor device with different gate structures, in accordance with some embodiments.

FIG. 2 is a flow diagram of a method for fabricating a semiconductor device with different gate structures, in accordance with some embodiments.

FIGS. 3A-15B illustrate cross-sectional views of a semiconductor device with different gate structures at various stages of its fabrication process, in accordance with some embodiments.

FIG. 16 is a flow diagram of a method for fabricating a semiconductor device with different gate structures, in accordance with some embodiments.

FIGS. 17A-26B illustrate cross-sectional views of a semiconductor device with different gate structures at various stages of its fabrication process, in accordance with some embodiments.

FIGS. 27-28 illustrates device characteristics of a semiconductor device with different gate structures at various stages of its fabrication process, in accordance with some embodiments.

Illustrative embodiments will now be described with reference to the accompanying drawings. In the drawings, like reference numerals generally indicate identical, functionally similar, and/or structurally similar elements.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the process for forming a first feature over a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. As used herein, the formation of a first feature on a second feature means the first feature is formed in direct contact with the second feature. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

It is noted that references in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” “exemplary,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases do not necessarily refer to the same embodiment. Further, when a particular feature, structure or characteristic is described in connection with an embodiment, it would be within the knowledge of one skilled in the art to effect such feature, structure or characteristic in connection with other embodiments whether or not explicitly described.

It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by those skilled in relevant art(s) in light of the teachings herein.

In some embodiments, the terms “about” and “substantially” can indicate a value of a given quantity that varies within 5% of the value (e.g., ±1%, ±2%, ±3%, ±4%, ±5% of the value). These values are merely examples and are not intended to be limiting. The terms “about” and “substantially” can refer to a percentage of the values as interpreted by those skilled in relevant art(s) in light of the teachings herein.

The fin structures disclosed herein may be patterned by any suitable method. For example, the fin structures may be patterned using one or more photolithography processes, including double-patterning or multi-patterning processes. Double-patterning or multi-patterning processes can combine photolithography and self-aligned processes, allowing patterns to be created that have, for example, pitches smaller than what is otherwise obtainable using a single, direct photolithography process. For example, a sacrificial layer is formed over a substrate and patterned using a photolithography process. Spacers are formed alongside the patterned sacrificial layer using a self-aligned process. The sacrificial layer is then removed, and the remaining spacers may then be used to pattern the fin structures.

The required gate voltage—the threshold voltage (VO—to turn on a field effect transistor (FET) can depend on the semiconductor material of the FET channel region and/or the effective work function (EWF) value of a gate structure of the FET. For example, for an n-type FET (NFET), reducing the difference between the EWF value(s) of the NFET gate structure and the conduction band energy of the material (e.g., 4.1 eV for Si or 3.8 eV for SiGe) of the NFET channel region can reduce the NFET threshold voltage. For a p-type FET (PFET), reducing the difference between the EWF value(s) of the PFET gate structure and the valence band energy of the material (e.g., 5.2 eV for Si or 4.8 eV for SiGe) of the PFET channel region can reduce the PFET threshold voltage. The EWF values of the FET gate structures can depend on the thickness and/or material composition of each of the layers of the FET gate structure. As such, FETs can be manufactured with different threshold voltages by adjusting the thickness and/or material composition of the FET gate structures.

Due to the increasing demand for multi-functional low power portable devices, there is an increasing demand for FETs with lower and/or different threshold voltages, such as threshold voltages lower than 200 mV. One way to achieve multi-Vt devices with low threshold voltages in FETs can be with different work function metal (WFM) layer thicknesses greater than about 4 nm (e.g., about 5 nm to about 10 nm) in the gate structures. However, the different WFM layer thicknesses can be constrained by the FET gate structure geometries. Also, depositing different WFM layer thicknesses can become increasingly challenging with the continuous scaling down of FETs (e.g., GAA FETs, finFETs, and/or MOSFETs).

The present disclosure provides example multi-Vt devices with FETs (e.g., finFETs) having low threshold voltages different from each other and provides example methods of forming such FETs on the same substrate. The example methods form NFETs and PFETs with WFM layer of similar thicknesses, but with lower and/or different threshold voltages on the same substrate. These example methods can be more cost-effective (e.g., cost reduced by about 20% to about 30%) and time-efficient (e.g., time reduced by about 15% to about 20%) in manufacturing reliable FET gate structures with lower and/or different threshold voltages than other methods of forming FETs with similar dimensions and threshold voltages on the same substrate. In addition, these example methods can form FET gate structures with much smaller dimensions (e.g., thinner gate stacks) than other methods of forming FETs with similar threshold voltages.

In some embodiments, NFETs and PFETs with different gate structure configurations, but with similar WFM layer thicknesses can be selectively formed on the same substrate to achieve lower and/or different threshold voltages. The different gate structures can have high-K (HK) gate dielectric layers doped with different metallic dopants. The different metal dopants can induce dipoles of different polarities and/or concentrations at interfaces between the HK gate dielectric layers and interfacial oxide (IO) layers. The dipoles of different polarities and/or concentrations result in gate structures with different EWF values and threshold voltages. Thus, controlling the dopant materials and/or concentrations in the HK gate dielectric layers can tune the EWF values of the NFET and PFET gate structures, and as a result can adjust the threshold voltages of the NFETs and PFETs without varying the WFM layer thicknesses. In some embodiments, instead of the doped HK gate dielectric layer, PFET gate structure can include a metallic oxide layer interposed between the HK gate dielectric and the IO layer to induce dipoles between the HK gate dielectric layer and the IO layer.

FIG. 1A illustrates an isometric view of a semiconductor device 100 with PFET 102P and NFET 102N, according to some embodiments. PFET 102P and NFET 102N can have different cross-sectional views, as illustrated in FIGS. 1B-1E, according to various embodiments. FIGS. 1B-1E illustrate cross-sectional views of PFET 102P and NFET 102N along respective lines A-A and B-B of FIG. 1A. FIGS. 1B-1E illustrate cross-sectional views of semiconductor device 100 with additional structures that are not shown in FIG. 1A for simplicity. The discussion of elements of PFET 102P and NFET 102N with the same annotations applies to each other, unless mentioned otherwise.

Referring to FIG. 1A, NFET 102N can include an array of gate structures 112N disposed on fin structure 106N, and PFET 102P can include an array of gate structures 112P disposed on fin structure 106P. NFET 102N can further include an array of S/D regions 110N disposed on portions of fin structure 106N that are not covered by gate structures 112N. Similarly, PFET 102P can further include an array of epitaxial S/D regions 110P disposed on portions of fin structure 106P that are not covered by gate structures 112P.

Semiconductor device 100 can further include gate spacers 114, shallow trench isolation (STI) regions 116, etch stop layers (ESLs) 117, and interlayer dielectric (ILD) layers 118. In some embodiments, gate spacers 114, STI regions 116, ESLs 117, and ILD layers 118 can include an insulating material, such as silicon oxide, silicon nitride (SiN), silicon carbon nitride (SiCN), silicon oxycarbon nitride (SiOCN), and silicon germanium oxide. In some embodiments, gate spacers 114 can have a thickness of about 2 nm to about 9 nm for adequate electrical isolation of gate structures 112N and 112P from adjacent structures.

Semiconductor device 100 can be formed on a substrate 104 with PFET 102P and NFET 102N formed on different regions of substrate 104. There may be other FETs and/or structures (e.g., isolation structures) formed between PFET 102P and NFET 102N on substrate 104. Substrate 104 can be a semiconductor material, such as silicon, germanium (Ge), silicon germanium (SiGe), a silicon-on-insulator (SOI) structure, and a combination thereof. Further, substrate 104 can be doped with p-type dopants (e.g., boron, indium, aluminum, or gallium) or n-type dopants (e.g., phosphorus or arsenic). In some embodiments, fin structures 106P-106N can include a material similar to substrate 104 and extend along an X-axis.

Referring to FIGS. 1B-1C, PFET-NFET 102P-102N can include S/D regions 110P-110N and gate structures 112P-112N. For PFET 102P, S/D regions 110P can include an epitaxially-grown semiconductor material, such as Si and SiGe, and p-type dopants, such as boron and other suitable p-type dopants. For NFET 102N, S/D regions 110N can include an epitaxially-grown semiconductor material, such as Si, and n-type dopants, such as phosphorus and other suitable n-type dopants.

Gate structures 112P-112N can be multi-layered structures. Gate structures 112P-112N can include (i) gate oxide structures 122P-122N disposed on respective fin structures 106P-106N, (ii) WFM layers 124P-124N disposed on respective gate oxide structures 122P-122N, and (iii) gate metal fill layers 126P-126N disposed on respective WFM layers 124P-124N.

Referring to FIG. 1B, in some embodiments, gate oxide structure 122P can include (i) an IO layer 128P disposed on fin structure 106P, (ii) a metallic oxide layer 132P disposed on IO layer 128P, (iii) a dipole layer 130P disposed at an interface between IO layer 128P and metallic oxide layer 132P, (iv) a first HK gate dielectric layer 134P disposed on metallic oxide layer 132P, and (v) a second HK gate dielectric layer 136P disposed on first HK gate dielectric layer 134P.

TO layer 128P can include an oxide of the material of fin structure 106P, such as silicon oxide (SiO₂), silicon germanium oxide (SiGeOx), and germanium oxide (GeOx). The material of metallic oxide layer 132P can induce the formation of p-type dipoles in dipole layer 130P. Dipole layer 130P can include p-type dipoles of metallic ions from metallic oxide layer 132P and oxygen ions from IO layer 128P. Metallic oxide layer 132P can include oxides of metallic materials that have electronegativity values greater than the electronegativity values of metallic or semiconductor materials included in first HK gate dielectric layer 134P. In addition, metallic oxide layer 132P can include oxide materials that have oxygen areal densities greater than the oxygen areal densities of oxide materials included in first HK gate dielectric layer 134P. As used herein, the term “oxygen areal density” of an oxide material refers to an atomic concentration of oxygen atoms per unit area of the oxide material.

The larger electronegativity value and oxygen areal density of metallic oxide layer 132P can induce stronger p-type dipoles in dipole layer 130P compared to dipoles induced at an interface between IO layer 128P and first HK gate dielectric layer 134P in the absence of metallic oxide layer 132P. As stronger p-type dipoles can result in lower threshold voltages for PFETs, the use of metallic oxide layer 132P can form PFET 102P with a threshold voltage lower than about 200 mV (e.g., about 150 mV, 100 mV, or 50 mv). In some embodiments, metallic oxide layer 132P can include oxides of metallic materials from group 13 of the periodic table, such as gallium oxide (Ga₂O₃), aluminum oxide (Al₂O₃), and indium oxide (In₂O₃), when first HK gate dielectric layer 134P includes HfO₂. In some embodiments, metallic oxide layer 132P with Ga₂O₃ can provide better device performance than metallic oxide layer 132P with Al₂O₃. In some embodiments, dipole layer 130P can include Ga—O, Al—O, or In—O p-type dipoles when metallic oxide layer 132P includes Ga₂O₃, Al₂O₃, and In₂O₃, respectively. In some embodiments, metallic oxide layer 132P can have a thickness ranging from about 0.5 nm to about 3 nm. The thickness of metallic oxide layer 132P below 0.5 nm may not induce the formation of dipoles in dipole layer 130P. On the other hand, if the thickness of metallic oxide layer 132P above 3 nm, diffusion of metallic atoms from metallic oxide layer 132P may degrade first and second HK gate dielectric layers 134P-136P, and consequently device performance.

First and second HK gate dielectric layers 134P-136P can include high-k dielectric materials, such as hafnium oxide (HfO₂), titanium oxide (TiO₂), hafnium zirconium oxide (HfZrO), tantalum oxide (Ta₂O₃), hafnium silicate (HfSiO₄), zirconium oxide (ZrO₂), and zirconium silicate (ZrSiO₂). In some embodiments, first and second HK gate dielectric layers 134P-136P can include materials similar to or different from each other. In some embodiments, first and second HK gate dielectric layers 134P-136P can have thicknesses similar to or different from each other. In some embodiments, first and second HK gate dielectric layers 134P-136P can be undoped.

In some embodiments, p-type WFM (pWFM) layer 124P can include substantially Al-free (e.g., with no Al) (i) Ti—based nitrides or alloys, such as TiN, TiSiN, titanium gold (Ti—Au) alloy, titanium copper (Ti—Cu) alloy, titanium chromium (Ti—Cr) alloy, titanium cobalt (Ti—Co) alloy, titanium molybdenum (Ti—Mo) alloy, and titanium nickel (Ti—Ni) alloy; (ii) Ta—based nitrides or alloys, such as TaN, TaSiN, Ta—Au alloy, Ta—Cu alloy, Ta—W alloy, tantalum platinum (Ta—Pt) alloy, Ta—Mo alloy, Ta—Ti alloy, and Ta—Ni alloy; or (iii) a combination thereof. In some embodiments, pWFM layer 124P can include a thickness ranging from about 1 nm to about 3 nm. Other suitable dimensions of pWFM layer 124P are within the scope of the present disclosure. Gate metal fill layer 126P can include a suitable conductive material, such as tungsten (W), Ti, silver (Ag), ruthenium (Ru), molybdenum (Mo), copper (Cu), cobalt (Co), Al, iridium (Ir), nickel (Ni), metal alloys, and a combination thereof.

Referring to FIG. 1C, in some embodiments, gate oxide structure 122N can include (i) an IO layer 128N disposed on fin structure 106N, (ii) a first HK gate dielectric layer 134N disposed on IO layer 128N, (iii) a second HK gate dielectric layer 136N disposed on first HK gate dielectric layer 134N, and (iv) a dipole layer 130N disposed at an interface between IO layer 128P and first HK gate dielectric layer 134N.

IO layer 128N can include an oxide of the material of fin structure 106N, such as silicon oxide (SiO₂), silicon germanium oxide (SiGeOx), and germanium oxide (GeOx). In some embodiments, first HK gate dielectric layer 134N can include dopants of metals that have electronegativity values lower than the electronegativity values of metallic or semiconductor materials included in first HK gate dielectric layer 134N. In some embodiments, first HK gate dielectric layer 134N can include dopants of a rare-earth metal, such as Lanthanum (La), Yttrium (Y), Scandium (Sc), Cerium (Ce), Ytterbium (Yb), Erbium (Er), Dysprosium (Dy), and Lutetium (Lu). The metal dopants of first HK gate dielectric layer 134N can induce the formation of n-type dipoles in dipole layer 130N. Dipole layer 130N can include n-type dipoles of metal ions from the metal dopants and oxygen ions from IO layer 128N, such as La-O dipoles, when first HK gate dielectric layer 134N includes La dopants. The lower electronegativity value of the metal dopants of first HK gate dielectric layer 134N can induce stronger n-type dipoles in dipole layer 130N compared to dipoles induced at an interface between IO layer 128P and undoped first HK gate dielectric layer 134N. In some embodiments, first and second HK gate dielectric layers 134N-136N can include high-k dielectric materials similar to first and second HK gate dielectric layers 134P-136P

In some embodiments, nWFM layer 124N can include titanium aluminum (TiAl), titanium aluminum carbide (TiAlC), tantalum aluminum (TaAl), tantalum aluminum carbide (TaAlC), Al-doped Ti, Al-doped TiN, Al-doped Ta, Al-doped TaN, or a combination thereof. In some embodiments, nWFM layer 124N can include a thickness ranging from about 1 nm to about 3 nm. Other suitable dimensions of nWFM layer 124N are within the scope of the present disclosure. Gate metal fill layer 126N can include a conductive material similar to gate metal fill layer 126P.

Referring to FIG. 1D, in some embodiments, gate oxide structure 122P does not include metallic oxide layer 132P and includes first HK gate dielectric layer 135P with metal dopants instead of undoped first HK gate dielectric layer 134P (shown in FIG. 1B). Instead of metallic oxide layer 132P, the metal dopants of first HK gate dielectric layer 135P induces the formation of p-type dipoles in dipole layer 130P. Dipole layer 130P can include p-type dipoles of metal ions from the metal dopants of first HK gate dielectric layer 135P and oxygen ions from IO layer 128P. First HK gate dielectric layer 135P can include dopants of metals that have electronegativity values greater than the electronegativity values of metallic or semiconductor materials included in first HK gate dielectric layer 135P. In some embodiments, first HK gate dielectric layer 135P can include dopants of materials from group 13 of the periodic table, such as Ga, Al, and In, when first HK gate dielectric layer 135P includes HfO2. In some embodiments, dipole layer 130P can include Ga—O, Al—O, or In—O p-type dipoles when first HK gate dielectric layer 135P includes Ga, Al, and In dopants, respectively.

FIG. 1F shows the Hf, Ga, O₂, and Si concentration profiles 138, 140, 142, and 144 across first HK gate dielectric layer 135P and IO layer 128P along line C-C of FIG. 1D, when first HK gate dielectric layer 135P includes HfO₂ and Ga dopants and IO layer 128P includes SiO₂, according to some embodiments. As shown in FIG. 1F, the dopant concentration is higher within first HK gate dielectric layer 135P than in dipole layer 130P.

FIG. 2 is a flow diagram of an example method 200 for fabricating PFET-NFET 102P-102N with cross-sections as shown in FIGS. 1B-1C, according to some embodiments. For illustrative purposes, the operations illustrated in FIG. 2 will be described with reference to the example fabrication process for fabricating PFET-NFET 102P-102N as illustrated in FIGS. 3A-15B. FIGS. 3A-15B are cross-sectional views of PFET-NFET 102P-102N along lines A-A and B-B of FIG. 1A at various stages of fabrication, according to various embodiments. Operations can be performed in a different order or not performed depending on specific applications. It should be noted that method 200 may not produce complete PFET-NFET 102P-102N. Accordingly, it is understood that additional processes can be provided before, during, and after method 200, and that some other processes may only be briefly described herein. Elements in FIGS. 3A-15B with the same annotations as elements in FIGS. 1A-1C are described above.

In operation 205, polysilicon structures and S/D regions are formed on fin structures a PFET and NFET. For example, as shown in FIGS. 3A-3B polysilicon structures 312P-312N and S/D regions 110P-110N are formed on respective fin structure 106P-106N, which are formed on substrate 104. During subsequent processing, polysilicon structures 312P-312N can be replaced in a gate replacement process to form gate structures 112P-112N. After the formation of S/D regions 110P-110N, ESLs 117A and ILD layers 118 can be formed to form the structures of FIGS. 3A-3B.

Referring to FIG. 2 , in operation 210, gate openings are formed on the fin structures. For example, as shown in FIGS. 4A-4B, gate openings 412P-412N are formed on respective fin structures 106P-106N. The formation of gate openings 412P-412N can include etching polysilicon structures 312P-312N from the structures of FIGS. 3A-3B.

Referring to FIG. 2 , in operations 215-235, gate oxide structures are formed within the gate openings. For example, as described with reference to FIGS. 4A-12B, gate oxide structures 122P-122N (shown in FIGS. 1B-1C) are formed within respective gate openings 412P-412N.

Referring to FIG. 2 , in operation 215, IO layers are formed within the gate openings. For example, as shown in FIGS. 5A-5B, IO layers 128P-128N are formed within gate openings 412P-412N. In some embodiments, IO layers 128P-128N can be formed by exposing the surfaces of fin structures 106P-106N within respective gate openings 412P-412N to an oxidizing ambient. The oxidizing ambient can include a combination of ozone (O₃), a mixture of ammonia hydroxide, hydrogen peroxide, and water, and/or a mixture of hydrochloric acid, hydrogen peroxide, and water.

The subsequent formation of layers on IO layers 128P-128N in operations 220-240 are described with reference to FIGS. 6A-13B, which are enlarged views of regions 103P-103N shown in respective FIGS. 5A-5B.

Referring to FIG. 2 , in operation 220, a metallic oxide layer is selectively formed on the IO layer of the PFET. For example, as described with reference to FIGS. 6A-7B, metallic oxide layer 132P is formed on IO layer 128P. The selective formation of metallic oxide layer 132P can include sequential operations of (i) depositing a metallic oxide layer 132 on the structures of FIGS. 5A-5B to form the structures of FIGS. 6A-6B, and (ii) selectively removing the portion of metallic oxide layer 132 on IO layer 128N by using a lithographic patterning process on the structures of FIGS. 6A-6B to form the structures of FIGS. 7A-7B. Dipole layer 130P induced between metallic oxide layer 132 and IO layer 128N is removed when the portion of metallic oxide layer 132 on IO layer 128N is removed. The deposition of metallic oxide layer 132 can include depositing about 0.5 nm to about 3 nm layer of oxide of a metallic material (e.g., Ga, Al, or In) that have an electronegativity value greater than the electronegativity values of metallic or semiconductor materials (e.g., Hf, Zr, or Ti) included in first HK gate dielectric layer 134P. In addition, the layer of oxide (e.g., Ga₂O₃, Al₂O₃, or In₂O₃) can have an oxygen areal density greater than the oxygen areal density of the oxide material (e.g., HfO₂, ZrO₂, or TiO₂) included in first HK gate dielectric layer 134P.

Referring to FIG. 2 , in operation 225, a first HK gate dielectric layer with a first layer portion on the metallic oxide layer and a second layer portion on the IO layer of the NFET is formed. For example, as shown in FIGS. 8A-8B, a first HK gate dielectric layer with a first layer portion 134P (also referred to as “first HK gate dielectric layer 134P”) on metallic oxide layer 132P and a second layer portion 134N* (also referred to as “first HK gate dielectric layer 134N*”) on IO layer 128N is formed. In some embodiments, first HK gate dielectric layers 134P-134N* can be formed by depositing about 1 nm to about 2 nm of HfO₂ with an atomic layer deposition (ALD) process using hafnium chloride (HfCl₄) as a precursor at a temperature ranging from about 250° C. to about 350° C.

Referring to FIG. 2 , in operation 230, a doping process is selectively performed on the second layer portion of the first HK gate dielectric layer. For example, as described with reference to FIGS. 9A-11B, a doping process is selectively performed on first HK gate dielectric layer 134N*. The selective doping process can include sequential operations of (i) depositing a dopant source layer 946 on the structures of FIGS. 8A-8B to form the structures of FIGS. 9A-9B, (ii) selectively removing the portion of dopant source layer 946 on first HK gate dielectric layer 134P by using a lithographic patterning process on the structures of FIGS. 9A-9B to form the structures of FIGS. 10A-10B, (iii) performing a drive-in anneal process on the structures of FIGS. 10A-10B to form doped first HK gate dielectric layer 134N and dipole layer 130N, as shown in FIG. 11B, and (iv) removing dopant source layer 946 from the structure of FIG. 10B to form the structures of FIGS. 11A-11B.

The drive-in anneal process can implant metal dopants into first HK gate dielectric layer 134N* through a diffusion of metal atoms from dopant source layer 946 into first HK gate dielectric layer 134N*. The implanted metal dopants can induce the formation of dipole layer 130N. The drive-in anneal process can include annealing the structures of FIGS. 10A-10B at a temperature from about 600° C. to about 800° C. and at a pressure from about 1 torr to about 50 torr for a time period ranging from about 0.1 second to about 30 seconds. In some embodiments, the drive-in anneal process can include two anneal processes: (i) a soak anneal process at a temperature from about 600° C. to about 800° C. for a time period ranging from about 2 sec to about 60 sec and (ii) a spike anneal process at a temperature from about 700° C. to about 800° C. for a time period ranging from about 0.1 second to about 2 seconds.

The deposition of dopant source layer 946 can include depositing a layer of oxide of a rare-earth metal (e.g., La, Y, Sc, Ce, Yb, Er, Dy, or Lu) that have an electronegativity value lower than the electronegativity values of metallic or semiconductor materials (e.g., Hf, Zr, or Ti) included in first HK gate dielectric layer 134N. In addition, the layer of oxide (e.g., lanthanum oxide (La₂O₃), yttrium oxide (Y₂O₃), scandium oxide (Sc₂O₃), cerium oxide (CeO₂), ytterbium oxide (Yb₂O₃), erbium oxide (Er₂O₃), dysprosium oxide (Dy₂O₃), or lutetium oxide (Lu₂O₃)) can have an oxygen areal density smaller than the oxygen areal density of the oxide material (e.g., HfO₂, ZrO₂, or TiO₂) included in first HK gate dielectric layer 134N.

Referring to FIG. 2 , in operation 235, a second HK gate dielectric layer with first and second layer portions on the first and second layer portions of the first HK gate dielectric layer is formed. For example, as shown in FIGS. 12A-12B, a second HK gate dielectric layer with a first layer portion 136P (also referred to as “second HK gate dielectric layer 136P”) on first HK gate dielectric layer 134P and a second layer portion 136N (also referred to as “second HK gate dielectric layer 136N”) on first HK gate dielectric layer 134N is formed. In some embodiments, second HK gate dielectric layers 136P-136N can be formed by depositing about 5 nm to about 8 nm of HfO₂ with an atomic layer deposition (ALD) process using hafnium chloride (HfCl₄) as a precursor at a temperature ranging from about 250° C. to about 350° C. In some embodiments, second HK gate dielectric layers 136P-136N can be deposited thicker than first HK gate dielectric layers 134P-134N. In some embodiments, second HK gate dielectric layers 136P-136N can be about 1.5 times to about 3 times thicker than first HK gate dielectric layers 134P-134N. The thinner first HK gate dielectric layer 134N facilitates the doping of first HK gate dielectric layer 134N.

Referring to FIG. 2 , in operation 240, a pWFM layer is selectively formed on the first layer portion of the second HK gate dielectric layer and an nWFM layer is selectively formed on the second layer portion of the second HK gate dielectric layer. For example, as shown in FIGS. 13A-13B, pWFM layer 124P is selectively formed on second HK gate dielectric layer 136P and nWFM layer 124N is selectively formed on second HK gate dielectric layer 136N. The selective formation of pWFM 124P and nWFM layers 124N can be performed on the structures of FIGS. 12A-12B using lithographic patterning processes to form the structures of FIGS. 13A-13B.

Referring to FIG. 2 , in operation 245, gate metal fill layers are formed on the pWFM layer and the nWFM layer. For example, as described with reference to FIGS. 14A-15B, gate metal fill layers 126P and 126N are formed on respective pWFM layer 124P and nWFM layer 124N. The formation of gate metal fill layers 126P-126N can include sequential operations of (i) depositing a conductive layer 1426 on the structures of FIGS. 13A-13B to fill gate openings 412P-412N and form the structures of FIGS. 14A-14B, and (ii) performing a chemical mechanical polishing (CMP) process on the structures of FIGS. 14A-14B to form the structures of FIGS. 15A-15B with top surfaces of gate structures 112P-112N substantially coplanar with a top surface of ILD layer 118. In some embodiments, after the CMIP process, gate capping layers (not shown) on gate structures 112P-112N and contact structures on gate structures 112P-112N and S/D regions 110P-110N can be formed.

FIG. 16 is a flow diagram of an example method 1600 for fabricating PFET-NFET 102P-102N with cross-sections as shown in FIGS. 1D-1E, according to some embodiments. For illustrative purposes, the operations illustrated in FIG. 16 will be described with reference to the example fabrication process for fabricating PFET-NFET 102P-102N as illustrated in FIGS. 16A-26B. FIGS. 16A-26B are cross-sectional views of PFET-NFET 102P-102N along lines A-A and B-B of FIG. 1A at various stages of fabrication, according to various embodiments. Operations can be performed in a different order or not performed depending on specific applications. It should be noted that method 1600 may not produce complete PFET-NFET 102P-102N. Accordingly, it is understood that additional processes can be provided before, during, and after method 1600, and that some other processes may only be briefly described herein. Elements in FIGS. 16A-26B with the same annotations as elements in FIGS. 1A-1E are described above.

Referring to FIG. 16 , operations 1605-1615 are similar to operations 205-215 of FIG. 2 . After operation 1615, structures similar to the structures of FIGS. 5A-5B are formed. The subsequent formation of layers on IO layers 128P-128N (shown in FIGS. 5A-5B) in operations 1620-1640 are described with reference to FIGS. 17A-24B, which are enlarged views of regions 103P-103N shown in respective FIGS. 5A-5B.

Referring to FIG. 16 , in operations 1615-1635, gate oxide structures are formed within the gate openings. For example, as described with reference to FIGS. 17A-23B, gate oxide structures 122P-122N (shown in FIGS. 1D-1E) are formed within respective gate openings 412P-412N (shown in FIGS. 4A-4B).

Referring to FIG. 16 , in operation 1620, a first HK gate dielectric layer with first and second layer portions on respective IO layers of the PFET and NFET 15 formed. For example, as shown in FIGS. 17A-17B, a first HK gate dielectric layer with a first layer portion 134P* on IO layer 128P and a second layer portion 134N* on IO layer 128N is formed. In some embodiments, first and second layer portions 134P*-134N* can be formed by depositing about 1 nm to about 2 nm of HfO₂ with an atomic layer deposition (ALD) process using hafnium chloride (HfCl₄) as a precursor at a temperature ranging from about 250° C. to about 350° C.

Referring to FIG. 16 , in operation 1625, a doping process is selectively performed on the first layer portion of the first HK gate dielectric layer. For example, as described with reference to FIGS. 18A-20B, a doping process is selectively performed on first layer portion 134P*. The selective doping process can include sequential operations of (i) depositing a dopant source layer 1848 on the structures of FIGS. 17A-17B, as shown in FIGS. 18A-18B, (ii) selectively removing the portion of dopant source layer 1848 on second layer portion 134N* by using a lithographic patterning process on the structures of FIGS. 18A-18B to form the structures of FIGS. 19A-19B, (iii) performing a drive-in anneal process on the structures of FIGS. 19A-19B to form doped first HK gate dielectric layer 135P and dipole layer 130P, as shown in FIG. 20A, and (iv) removing dopant source layer 1848 from the structure of FIG. 19 to form the structures of FIGS. 20A-20B.

The drive-in anneal process can implant metallic dopants into first layer portion 134P* through diffusion of metallic atoms from dopant source layer 1848 into first layer portion 134P*. The implanted metallic dopants can induce the formation of dipole layer 130P. The drive-in anneal process can include annealing the structures of FIGS. 19A-19B at a temperature from about 600° C. to about 800° C. and at a pressure from about 1 torr to about 50 torr for a time period ranging from about 0.1 second to about 30 seconds. In some embodiments, the drive-in anneal process can include two anneal processes: (i) a soak anneal process at a temperature from about 600° C. to about 800° C. for a time period ranging from about 2 sec to about 60 sec and (ii) a spike anneal process at a temperature from about 700° C. to about 800° C. for a time period ranging from about 0.1 second to about 2 seconds.

FIG. 27 shows the Hf, Ga, O₂, and Si concentration profiles 138, 140, 142, and 144 along line D-D of FIG. 19A before the drive-in anneal process, when first layer portion 134P* includes HfO₂, dopant source layer 1848 includes Ga₂O₃, and IO layer 128P includes SiO₂, according to some embodiments. FIG. 28 shows the Hf, Ga, O₂, and Si concentration profiles 138, 140, 142, and 144 along line D-D of FIG. 19A after the drive-in anneal process. Prior to the drive-in anneal process, the peak concentration of Ga atoms is within the region of dopant source layer 1848, as shown in FIG. 27 . Following the drive-in anneal process, the peak concentration of Ga atoms shifts to the region of first HK gate dielectric layer 135P, as shown in FIG. 28 , thus indicating the implantation of Ga dopants in first HK gate dielectric layer 135P.

The deposition of dopant source layer 1848 can include depositing a layer of oxide of a metallic material (e.g., Ga, Al, or In) that have an electronegativity value greater than the electronegativity values of metallic or semiconductor materials (e.g., Hf, Zr, or Ti) included in first HK gate dielectric layer 135P. In addition, the layer of oxide (e.g., Ga₂O₃, Al₂O₃, or In₂O₃) can have an oxygen areal density greater than the oxygen areal density of the oxide material (e.g., HfO₂, ZrO₂, or TiO₂) included in first HK gate dielectric layer 135P.

Referring to FIG. 16 , in operation 1630, a doping process is selectively performed on the second layer portion of the first HK gate dielectric layer. For example, as described with reference to FIGS. 21A-23B, a doping process is selectively performed on second layer portion 134N*. The selective doping process can include sequential operations of (i) depositing a dopant source layer 946 on the structures of FIGS. 20A-20B to form the structures of FIGS. 21A-21B, (ii) selectively removing the portion of dopant source layer 946 on first HK gate dielectric layer 135P by using a lithographic patterning process on the structures of FIGS. 21A-21B to form the structures of FIGS. 22A-22B, (iii) performing a drive-in anneal process on the structures of FIGS. 22A-22B to form doped first HK gate dielectric layer 134N and dipole layer 130N, as shown in FIG. 23B, and (iv) removing dopant source layer 946 from the structure of FIG. 22B. The deposition of dopant source layer 946 and the drive-in anneal process is similar to those described in operation 230.

Referring to FIG. 16 , in operation 1635, a second HK gate dielectric layer with first and second layer portions on the doped first and second layer portions of the first HK gate dielectric layer is formed. For example, as shown in FIGS. 23A-23B, a second HK gate dielectric layer with a first layer portion 136P (also referred to as “second HK gate dielectric layer 136P”) on first HK gate dielectric layer 135P and a second layer portion 136N (also referred to as “second HK gate dielectric layer 136N”) on first HK gate dielectric layer 134N is formed. Second HK gate dielectric layers 136P-136N can be formed in an operation similar to that described in operation 235.

Referring to FIG. 16 , in operation 1640, a pWFM layer is selectively formed on the first layer portion of the second HK gate dielectric layer and an nWFM layer is selectively formed on the second layer portion of the second HK gate dielectric layer. For example, as shown in FIGS. 24A-24B, pWFM layer 124P is selectively formed on second HK gate dielectric layer 136P and nWFM layer 124N is selectively formed on second HK gate dielectric layer 136N. The selective formation of pWFM 124P and nWFM layers 124N can be performed on the structures of FIGS. 23A-23B using lithographic patterning processes to form the structures of FIGS. 24A-24B.

Referring to FIG. 16 , in operation 1645, gate metal fill layers are formed on the pWFM layer and the nWFM layer. For example, as described with reference to FIGS. 25A-26B, gate metal fill layers 126P and 126N are formed on respective pWFM layer 124P and nWFM layer 124N. The formation of gate metal fill layers 126P-126N is similar to that described in operation 245.

The present disclosure provides example multi-Vt devices with FETs (e.g., PFET 102P and NFET 102N) having low threshold voltages different from each other and provides example methods of forming such FETs on the same substrate. The example methods form NFETs and PFETs with WFM layers (e.g., pWFM layer 124P and nWFM layer 124N) of similar thicknesses, but with lower and/or different threshold voltages on the same substrate. These example methods can be more cost-effective (e.g., cost reduced by about 20% to about 30%) and time-efficient (e.g., time reduced by about 15% to about 20%) in manufacturing reliable FET gate structures with lower and/or different threshold voltages than other methods of forming FETs with similar dimensions and threshold voltages on the same substrate. In addition, these example methods can form FET gate structures with smaller dimensions (e.g., thinner gate stacks) than other methods of forming FETs with similar threshold voltages.

In some embodiments, NFETs and PFETs with different gate structure configurations (e.g., gate structures 112P-112N), but with similar WFM layer thicknesses, can be selectively formed on the same substrate (e.g., substrate 104) to achieve lower and/or different threshold voltages. The different gate structures can have HK gate dielectric layers (e.g., HK gate dielectric layers 135P and 134N) doped with different metallic dopants (e.g., Ga dopants and La dopants). The different metal dopants can induce dipoles of different polarities and/or concentrations in dipole layers (e.g., dipole layers 130P-130N) at interfaces between the HK gate dielectric layers and IO layers. The dipoles of different polarities and/or concentrations result in gate structures with different EWF values and threshold voltages. Thus, controlling the dopant materials and/or concentrations in the HK gate dielectric layers can tune the EWF values of the NFET and PFET gate structures, and as a result can adjust the threshold voltages of the NFETs and PFETs without varying the WFM layer thicknesses. In some embodiments, instead of the doped HK gate dielectric layer, PFET gate structure can include a metallic oxide layer (e.g., metallic oxide layer 132P) interposed between the HK gate dielectric (e.g., HK gate dielectric layer 134P) and the IO layer (e.g., IO layer 128P) to induce dipoles between the HK gate dielectric layer and the IO layer.

In some embodiments, a method includes forming a fin structure on a substrate, forming a gate opening on the fin structure, forming a metallic oxide layer within the gate opening, forming a first dielectric layer on the metallic oxide layer, forming a second dielectric layer on the first dielectric layer, forming a work function metal (WFM) layer on the second dielectric layer, and forming a gate metal fill layer on the WFM layer. The forming the first dielectric layer includes depositing an oxide material with an oxygen areal density less than an oxygen areal density of the metallic oxide layer.

In some embodiments, a method includes forming first and second fin structures on a substrate, forming first and second gate openings on the first and second fin structures, respectively, forming a first dielectric layer with first and second layer portions formed within the first and second gate openings, respectively, selectively doping the first layer portion with first dopants, wherein the first dopants have an electronegativity value greater than an electronegativity value of a metal or a semiconductor of the first dielectric layer, selectively doping the second layer portion with second dopants different from the first dopants, forming a second dielectric layer with first and second layer portions on the first and second layer portions of the first dielectric layer, and forming first and second gate metal fill layers over the first and second layer portions of the second dielectric layer, respectively. The second dopants have an electronegativity value less than an electronegativity value of the metal or the semiconductor of the first dielectric layer.

In some embodiments, a semiconductor device includes a substrate, a fin structure disposed on the substrate, a semiconductor oxide layer disposed on the fin structure, a metallic oxide layer disposed on the semiconductor oxide layer, a first dielectric layer disposed on the metallic oxide layer, a second dielectric layer disposed on the first dielectric layer, a work function metal (WFM) layer disposed on the second dielectric layer, and a gate metal fill layer on the WFM layer. A metallic material of the metallic oxide layer has an electronegativity value greater than an electronegativity value of a metal or a semiconductor the first dielectric layer.

The foregoing disclosure outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A method, comprising: forming a fin structure on a substrate; forming a gate opening on the fin structure; forming a metallic oxide layer within the gate opening; forming a first dielectric layer on the metallic oxide layer, wherein the forming the first dielectric layer comprises depositing an oxide material with an oxygen areal density less than an oxygen areal density of the metallic oxide layer; forming a second dielectric layer on the first dielectric layer; forming a work function metal (WFM) layer on the second dielectric layer; and forming a gate metal fill layer on the WFM layer.
 2. The method of claim 1, wherein the forming the metallic oxide layer comprises depositing an oxide of a metallic material with an electronegativity value greater than an electronegativity value of a metal or a semiconductor of the first dielectric layer.
 3. The method of claim 1, wherein the forming the metallic oxide layer comprises depositing an oxide of a metallic material that is different from a metallic material of the second dielectric layer.
 4. The method of claim 1, further comprising forming an interfacial oxide layer on the fin structure.
 5. The method of claim 4, wherein the forming the metallic oxide layer comprises depositing the metallic oxide layer on the interfacial oxide layer.
 6. The method of claim 1, wherein the forming the metallic oxide layer comprises depositing an oxide of gallium, aluminum, or indium.
 7. The method of claim 1, wherein the forming the second dielectric layer comprises depositing the second dielectric layer with a thickness greater than a thickness of the first dielectric layer.
 8. A method, comprising: forming first and second fin structures on a substrate; forming first and second gate openings on the first and second fin structures, respectively; forming a first dielectric layer with first and second layer portions formed within the first and second gate openings, respectively; selectively doping the first layer portion with first dopants, wherein the first dopants have an electronegativity value greater than an electronegativity value of a metal or a semiconductor of the first dielectric layer; selectively doping the second layer portion with second dopants different from the first dopants, wherein the second dopants have an electronegativity value less than an electronegativity value of the metal or the semiconductor of the first dielectric layer; forming a second dielectric layer with first and second layer portions on the first and second layer portions of the first dielectric layer; and forming first and second gate metal fill layers over the first and second layer portions of the second dielectric layer, respectively.
 9. The method of claim 8, wherein the selectively doping the first layer portion with the first dopants comprises: forming a metallic oxide layer on the first and second layer portions of the first dielectric layer; removing a portion of the metallic oxide layer on the second layer portion of the first dielectric layer; and performing an annealing process.
 10. The method of claim 9, wherein the forming the metallic oxide layer comprises depositing an oxide material with an oxygen areal density greater than an oxygen areal density of an oxide material of the first dielectric layer.
 11. The method of claim 9, wherein the forming the metallic oxide layer comprises depositing an oxide of gallium, aluminum, or indium.
 12. The method of claim 8, wherein the selectively doping the second layer portion with the second dopants comprises: forming a rare-earth metal oxide layer on the first and second layer portions of the first dielectric layer; removing a portion of the rare-earth metal oxide layer on the first layer portion of the first dielectric layer; and performing an annealing process.
 13. The method of claim 12, wherein the forming the rare-earth metal oxide layer comprises depositing an oxide material with an oxygen areal density less than an oxygen areal density of an oxide material of the first dielectric layer.
 14. The method of claim 8, further comprising: selectively forming a p-type work function metal (pWFM) layer on the first layer portion of the second dielectric layer; and selectively forming an n-type work function metal (nWFM) layer on the second layer portion of the second dielectric layer.
 15. The method of claim 8, wherein the forming the second dielectric layer comprises depositing the second dielectric layer with a thickness greater than a thickness of the first dielectric layer.
 16. A semiconductor device, comprising: a substrate; a fin structure disposed on the substrate; a semiconductor oxide layer disposed on the fin structure; a metallic oxide layer disposed on the semiconductor oxide layer; a first dielectric layer disposed on the metallic oxide layer, wherein a metallic material of the metallic oxide layer has an electronegativity value greater than an electronegativity value of a metal or a semiconductor the first dielectric layer; a second dielectric layer disposed on the first dielectric layer; a work function metal (WFM) layer disposed on the second dielectric layer; and a gate metal fill layer on the WFM layer.
 17. The semiconductor device of claim 16, further comprising a dipole layer disposed at an interface between the metallic oxide layer and the semiconductor oxide layer.
 18. The semiconductor device of claim 17, wherein the dipole layer comprises a metallic atom of the metallic oxide layer and an oxygen atom of the semiconductor oxide layer.
 19. The semiconductor device of claim 16, wherein the second dielectric layer has a thickness greater than a thickness of the first dielectric layer.
 20. The semiconductor device of claim 16, wherein an oxygen areal density of the metallic oxide layer is greater than an oxygen areal density of the first dielectric layer. 